This work is concerned with the detailed kinetic mechanism of myosin ATPase and the possible relationship of the elementary kinetic steps to energy transformation in muscle contraction. The proposed study will used both intrinsic and extrinsic fluorophores to provide optical signals in following the reactions which the enzyme is engaged in. The specific physical tools to be used in this work include (1) stopped-flow and chemical relaxation spectrometry and (2) static and nanosecond fluorescence spectroscopy. With these tools we will (1) investigate the reaction steps that are involved in the cleavage of ATP catalyzed by myosin and actomyosin and (2) establish whether and how one of the myosin light chain influences the overall actomyosin ATPase mechanism.